A 74-year-old man sat before a Baltimore Circuit Court jury in a wheelchair yesterday, reaching out with two maimed arms to show how he unwittingly picked up an explosive paint can that nearly took his life in November.

Calling himself "a durn fool" for being trusting, Frank Busnuk told how answering a 4 a.m. knock on the door of his rowhouse in the 2100 block of E. Lombard St. ended with eight months in the hospital, lost limbs and blindness in one eye.

Two of Mr. Busnuk's neighbors -- Michael Williams, 17, and James Wells, 18 -- are on trial with Ronald Goldstein, Mr. Wells' 44-year-old uncle, on attempted murder and several related offenses in the Nov. 18 explosion.

Two other young men -- Joseph Wells, James Wells' 17-year-old brother, and James Bynaker, 16 -- have been charged in juvenile court, where proceedings are closed.

In an opening statement yesterday, prosecutor William D. McCollum Jr. said the group meant the bomb for Mr. Busnuk's son Paul, who had yelled at the group about a loud party the week before and told police about a broken car window.

Mr. McCollum said the bomb was built at Mr. Goldstein's home the day after the party, and rigged on the roof of Paul Busnuk's car six days later. It was filled with "BBs, nails, bolts, you name it," the prosecutor said.

He said an explosives expert who had investigated the Oklahoma City bombing would testify to the power of the device.

"This bomb was designed with one purpose in mind; this bomb was designed to hurt people," Mr. McCollum said.

The prosecutor acknowledged that his witnesses "weren't the best," and that he didn't get along with an important one -- Joseph Wells.

Indeed, defense attorneys told the jury that Joseph Wells already has given investigators six different versions of who was involved in the bombing, in exchange for placement in a juvenile facility in the Boston area.

In cross-examination of Frank Busnuk, defense attorneys also established that the victim did not see who left the bomb.

Frank Busnuk described three loud knocks on his door just after 4 a.m., and his sleepy reply that he would be right there.

"It sounded like somebody was in dire straits," he said. "I thought it was a joke, you know, after I didn't see anybody. I thought somebody was playing tricks."

Still in a daze, he got dressed and went outside to see if he could spot anyone on the street. All he saw were several shadows half a block away. What he did see was a paint can on the roof of his son's Thunderbird -- so he went to pick it up.

"That thing blew to -- I didn't know what happened," Mr. Busnuk said. "I called for my son to call the ambulance. As you sit here, here's the results."

His left arm has been amputated above the elbow. His right hand was reconstructed with three fingers, and another finger reattached as a thumb. Small fragments of BB pellets still are lodged in his face.

Paul Busnuk wept as he described hearing the explosion and finding his father bleeding on the street. He said the blast destroyed his car, broke windows in the house and scattered debris inside that he continued to find for months.